1. Field of the Invention
This invention relates to water cooling towers and particularly fill structure for bringing water to be cooled into direct contact with an airstream for evaporative cooling of the liquid.
Cooling towers primarily fall into two principal categories; those involving countercurrent flow of air and water and towers of the crossflow type wherein air flow is essentially perpendicular to the path of water travel. Crossflow towers offer advantages in many instances because of the ability to introduce cooling air across the entire vertical height of the tower casing whereas counterflow towers require that the cooling air be drawn in below the fill assembly. Splash type as well as film type fills have been used in crossflow towers, but excessive static pressure drop has limited the use of film fills in most commercial applications. As a consequence, splash type fill was the heat exchange medium of choice in crossflow towers, especially those categorized as industrial units used in utility and process applications.
In recent years, the energy costs in pumping water to be cooled to a level for delivery into the hot water distribution basin of crossflow cooling towers has become an important factor in overall tower design. The lower the pumping head, the more cost effective the tower operation is from an operating standpoint. However, splash type fill assemblies require an adequate fill volume for cooling efficiency thus presenting a minimum height which dictates indirectly the pumping head for a particular tower configuration.
Therefore, there has been a compelling need for a crossflow cooling tower which retains the inherent advantages of that configuration but which has a minimum pumping head for hot water to be cooled without a deleterious effect on cooling efficiency.
2. Description of the Prior Art
Heretofore, the use of film fill sheets in crossflow cooling towers has largely been limited to smaller towers where the overall size of the tower for shipment as a completed package is an important consideration and the cooling of large volumes of water under varying ambient conditions has not been a controlling design parameter. Efforts to incorporate film fill into large industrial type towers has not met with significant success principally because of the difficulty in obtaining an optimum balance between exposure of water to cooling air without undue static pressure drop. Also, for economics of manufacture and retention of combustion resistant properties, it has been recognized that the fill sheet should be of such nature that it may be fabricated of a synthetic resin such as polyvinylchloride or the equivalent and that construction thereof may be accomplished using straightforward manufacturing techniques and equipment involving minimum tooling costs with maximum product output, as for example by the utilization of vacuum forming techniques conventional in the plastics industry.
One type of film fill heretofore suggested has embodied a chevron pattern formed in the sheet with the fill units disposed vertically for flow of water thereover essentially as a liquid film and with the fill sheets disposed in horizontally spaced relationship for flow of air therepast in crossflow relationship to the water. However, until the present invention, it had been assumed that chevron fill sheets had reached a level of optimization that defied significant further improvement.
To put the importance of the present invention into perspective, it is well known in the cooling tower field that it is beyond practical expectations to make changes in fan design which would use the same horsepower but produce improvement in cooling performance of an order of magnitude approaching percentage levels of as much as about 5% or the like.
An exemplary chevron pattern film fill sheet is depicted in U.S. Pat. No. 3,733,063 issued to the assignee of this application May 15, 1973. In that fill sheet, the chevron pattern consists of a series of serpentine ridges extending from the normally uppermost edge of the fill sheet to the lowermost margin thereof with the chevron sections alternately facing the air inlet and air outlet portions thereof respectively thereby increasing the dwell time of the water as it flows downwardly over the sheet. Integral knobs are provided in the sheet which project outwardly therefrom in opposite directions which function as spacers for maintaining the film fill sheets in proper horizontal spaced relationship when located in pack-defining configuration. In this construction, the knobs located in adjacent aligned relationship were joined by an adhesive to provide a self-sustaining assembly of fill sheets.
Another type of film fill sheet spacer structure of integral construction is shown in U.S. Pat. No. 4,320,073 assigned to the assignee of this application and here again, although the construction has enjoyed substantial commercial usage, relatively close alignment between the sheets in adjacent relationship was required to assure proper inter-engagement of the spacers one to another.
In summary, although the film fill sheets heretofore employed by the assignee hereof embodying a chevron pattern and incorporating spacer knobs or projections as depicted in the patents referenced above, were recognized as significant improvements in the art, use thereof in the field presented certain handling problems either from the standpoint that the packs had to be glued at the point of manufacture or assembled on site with very close spacer alignment being required from sheet to sheet of the pack, and compromises were known to exist in the designs relative to cooling capacity as a function of static air pressure drop attributable to the use of a film type fill as opposed to a splash fill assembly.
U.S. Pat. No. 3,540,702 also depicts a chevron type fill pattern but the sheet itself is bent in a transverse serpentine fashion so that the bent portions of the adjacent sheet may be joined to form a cellular network, U.S. Pat. No. 3,286,999 in FIG. 3b thereof illustrates a fill pattern somewhat similar to that shown in the referenced '063 patent. The disclosure fails to indicate that the chevron pattern should be of critical dimensions or that the sheets should be of a relatively narrow spacing range therebetween.